1. Field of the Invention
The present invention generally relates to circularly polarized antenna arrays and, more particularly, to feed networks for circularly polarized antenna arrays.
2. Description of the Related Art
Circularly polarized planar antennas have been widely used for various applications such as a phased array antennas, mobile antennas, and for satellite antennas. In many cases, the antennas are required to support simultaneous dual polarization, where a sequential signal rotation and phase shift technique has proven to provide wide band circular polarization and low VSWR characteristics. Such dual polarization is used in direct broadcast satellite television systems to enable a single antenna to be used to simultaneously receive multiple channels.
More particularly, circular polarization in planar antenna arrays is accomplished by the system having a plurality of xe2x80x9cpatchxe2x80x9d antennas where a linearly polarized signal is coupled to each of the antenna elements. The signal is applied to the elements in a sequentially switched pattern to achieve circular polarization in either right-hand or left-hand form. However, such switched systems require sophisticated electronics and a substantial amount of microstrip or stripline circuitry to couple the RF signals to the antenna elements. Such circuit complexity results in substantial crosstalk between antenna elements and distortion of the antenna pattern.
Therefore, there is a need in the art for a simple feed network for a dual circular polarized antenna array.
The present invention is a planar polarizer feed network comprising a six port network having two input ports and four output ports. The output ports are designed to have the same amplitude while their phases are sequentially offset by 90 degrees when fed from a first input port or by minus 90 degrees when fed from a second input port. In one embodiment of the invention, each output port is coupled to an aperture coupled antenna element comprising a slot and a patch antenna element. In this arrangement, an RF signal may be coupled to each of the two input ports to couple properly phased signals to each of the four antenna elements to simultaneously form both right-hand and left-hand polarized signal emitted from a planar array of antenna elements.